Acquisition of Laser Ablation System to Quantify Matrix and Grain-boundary Trace Element Partitioning in Olivine and Pyroxenes: an Integrated Bulk and In Situ Approach

学术价值：岩浆和熔融固体残留物的微量元素特征可以成为破译地球上熔融和岩浆分离物理过程的有力工具。然而，只有当这些微量元素在矿物和熔体之间的分配得到很好的理解时，这些工具才能使用。目标是研究地幔中主要矿物相的微量元素分配，地幔是大多数熔融发生的地方。重点将放在橄榄石和正辉石上，它们是上地幔的主要矿物，但在划分方面了解最少。由于熔体污染和分析困难（橄榄石和正辉石中的微量元素浓度通常很低），与斜辉石相比，对分异的理解较差。为了避免熔体污染的影响，建立了橄榄石、正辉石和斜辉石基质在亚固体条件下的微量元素分配半理论模型，并利用地幔捕虏体对其进行了标定。然后，这些亚固体基质分配系数将根据温度进行校正，并与已知的斜辉石/熔体分配系数相关，从而得出一套一致的上地幔相矿物基质/熔体分配系数。接下来将测试最近的一个假设，即矿物晶界（例如，边缘）是微量元素的重要储存库，这是由于晶粒内部（基质）和晶界之间的平衡分配。将通过量化与上述矩阵划分理论的偏差来评估晶界划分。Rice现有的质谱设备（ICP-MS）将增加激光烧蚀能力，从而能够测量基质分配系数和筛选不平衡样品，从而促进这两个步骤。更广泛的影响：本研究的组成部分将用于本科生研究。获得激光器也将有利于其他正在进行的研究，并通过扩大莱斯大学和休斯顿地区其他机构的研究项目的广度，帮助吸引更多的本科生从事研究。

0549268LeeIntellectual merit: Trace element signatures of magmas and the solid residues of melting can be powerful tools for deciphering the physical processes of melting and magma segregation on Earth. However, these tools can only be used if the partitioning of such trace elements between minerals and melt is well understood. The goal is to investigate trace element partitioning of major mineral phases in the mantle, where most melting takes place. Emphasis will be on olivine and orthopyroxene, which are the dominant minerals in the upper mantle, but the least understood in terms of partitioning. This poorer understanding of partitioning compared to that of clinopyroxene is due to contamination effects from melts and analytical difficulties (trace element concentrations in olivine and orthopyroxene are often very low). To avoid melt contamination effects, a semi-theoretical model for trace element partitioning between olivine, orthopyroxene and clinopyroxene matrices at subsolidus conditions is developed and calibrated using mantle xenoliths. These subsolidus matrix partition coefficients will then be corrected-up for temperature and related to known clinopyroxene/melt partition coefficients, yielding a consistent set of mineral matrix/melt partition coefficients for upper mantle phases. This will be followed by testing of a recent hypothesis that mineral grain boundaries (e.g., rims) are significant repositories for trace elements due to equilibrium partitioning between grain interiors (matrix) and boundaries. Grain boundary partitioning will be assessed by quantifying the deviation from matrix partitioning theory above. Both steps will be facilitated by the addition of laser ablation capabilities to existing mass spectrometry facilities at Rice (ICP-MS) by enabling the measurement of matrix partition coefficients and the screening of disequilibrium samples.Broader Impacts: Components of this study will be parsed out for undergraduate research. Acquisition of a laser will also benefit other ongoing studies as well as help to entice more undergraduates into doing research by expanding the breadth of research projects at Rice and other institutions in the Houston area.